As is known, one of the possibilities offered by personal communication systems, such as the above-mentioned GSM system, is the provision of location-based services, i.e. services based on determination of the position of a mobile cellular telephone owner in an area served by one or more Base Transceiver Stations (BTS)
This is possible because modern GSM mobile equipment s capable of measuring Base Transceiver Stations in its own cell and neighboring cells, detecting, storing and transmitting the respective information.
This information comprises:                1. National code (Mobile Country Code=MCC) pertaining to the serving cell;        2. Network code (Mobile Network Code=MNC) pertaining to the serving cell;        3. Local area code (Local Area Code=LAC) pertaining to the serving cell;        4. Serving cell identification (Cell ID);        5. Control channel signal intensity of serving cell (RxLev);        6. Control channel signal intensity of neighboring cells detected by the telephone (RxLev);        7. Frequency indexes (BCCH-FREQ=Broad Control Channel−Frequency) univocally corresponding to channel numbers (ARFCN=Absolute Radio Frequency Channel Number) and identification codes (BSIC=Base transceiver Station Identity Code) related to neighboring cell base stations.        
This information, consisting of numeric data, combined with the geographic positions of the Base Transceiver Stations, contained in a database generally provided by the mobile telephone operator, can be used by an appropriate calculation procedure to estimate the position of the GSM mobile equipment.
The described information is normally tracked by the mobile equipment via a SIM Toolkit type application, installed on the SIM card (“Subscriber Identity Module”), and compressed to be sent by means of SMS (Short Message System) messages to a remote Service Center.
Firstly, the received messages are decompressed and then fed into a processing system, called a “Location Engine,” which, by applying an appropriate algorithm, computes the geographical position of the mobile equipment. If required, the system either informs the mobile equipment of its position or utilizes it for a location-based service.
The need to reduce the number of SMS messages transmitted for each location request arises during the data exchange phase between mobile equipment and Service Center. This is necessary to satisfy the needs of all mobile telephone operators, who cannot afford excessive traffic on their network for a single application, and of users, who require cost-effectiveness.
Additionally, reducing the number of transmitted SMS text messages means significantly reducing the response time of each location-based service, thus providing a significant contribution to service quality.